This invention relates to retroreflectors, and more particularly to hollow retroreflectors used with surveying equipment.
Surveying equipment currently use light rays (i.e., lasers) to perform the measuring and calculating functions required when surveying. Surveying retroreflectors are used to receive an incident light ray and reflect that ray along a parallel path back to its source. Some surveying equipment detects the return of the light ray and, from the elapsed time, determine the distance between the source and the retroreflector. Because the light ray is reflected back to its source, the retroreflector must be made very accurately and to very close tolerances.
Some surveying equipment use hollow retroreflectors. One example of a hollow retroreflector is shown in U.S. Pat. No. 5,122,901, which is owned by PLX, Inc. and sold under the name “Omni-Wave”. The hollow retroreflector shown in this patent uses three reflecting panels which are set in a receptacle. The receptacle is then received in an outer casing. The reflecting panels are made of glass and have a reflective coating applied thereto. Because of the precision that is required, the three glass panels must be very accurately set in the receptacle. The precision and accuracy required of the hollow retroreflector makes this retroreflector very expensive and time consuming to produce. Further, because glass is used, it is fragile.
Opticon, of Billerica, produces another hollow retroreflector which uses an aluminum substrate rather than a glass substrate. The Opticon retroreflector uses a male master coated with a releasing agent and a reflective coating. A bonding agent is applied to the coating on the master, or on the surfaces of the part to which the reflective coating is to be applied. The master and the part are then brought together to bond the reflective coating to the aluminum substrate. This hollow retroreflector is also very expensive and time consuming to produce. Additionally, the reflective coating may not transfer well, leaving voids or finishes which are unacceptable.